Ask HN: How can I fix my sleep schedule?

I've had trouble getting to sleep at a reasonable hour my entire life. Lately, I go to sleep at ~3:00am and wake up at ~9:45am. I'd like to get 8+ hours of sleep and go to bed before midnight, but after countless attempts, my body always reverts back to this ~3:00am sleep schedule. I've tried everything: melatonin, not eating past 6pm, reducing caffeine intake, regular exercise, but none of it seems to have a lasting effect.

To anyone who has had a less-than-desirable sleep schedule, how did you fix it?

Thanks!